<!DOCTYPE html>
<html>
  <head>
    <title>Textarea test</title>
  </head>
  <body>
  <textarea rows="5" cols="20"></textarea>
    <script src='mouse-helper.js'></script>
    <script>
      globalThis.result = '';
      globalThis.textarea = document.querySelector('textarea');
      textarea.addEventListener('input', () => result = textarea.value, false);
    </script>
  </body>
</html>
